Round and amoeboid microglial cells in the neonatal rabbit brain

Summary

Round and amoeboid microglial cells in brains of neonatal rabbits have been studied with light and electron microscopy. They are present mainly in the white matter where there are large extracellular spaces, but a few occur in the vicinity of blood vessels in the basal ganglia. They are easily recognized by the shape of their processes. Both round and amoeboid cells are highly differentiated cells whose size and cytoplasmic vacuoles are similar to phagocytes. They lack the fibrils and microtubules of young nerve and glial cells and contain a rich complement of cytoplasmic organelles. Large numbers of lipid bodies and vacuoles are their most characteristic features. Small vacuoles are concentrated near the cell surface and contain material identical to that filling the extracellular space. They appear to arise as invaginations at the cell surface, to unite to form large vacuoles, and to increase in density as their contents are degraded. The role of these cells in the embryonic development of the brain is not clear and further work is in progress to establish their origin and fate.